It does what? lol you surprise me lauren,thats nowhere near how it works.
G theres one of two reasons why your idle is bouncing.
.
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1)as mentioned you have air in the cooling system
2)your coldstart waxstat valve is stuck open
Fault 1)The air has entered the system for one of a few reasons
a)you have a water leak somewhere,radiator,matrix,heater pipes etc
b)you have a cracked expansion bottle cap
c)the pressure cap is faulty
d)you have a head gasket fault
(mk1's can appear to be fine,will even idle perfectly but can still have a gasket fault)
e)faulty water pump
Simply bleeding it will temporarily cure the problem but it WILL return due to one of the above.
Fault 2)No matter if theres air in the system or not if the waxstat is stuck open you will get bouncing idle when the engine gets warm,this isnt as common as fault 1.
The bouncing idle happens because of a conflict.
.
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.if for whatever reason above the coldstart waxstat is open it allows extra air to be drawn past the throttle butterfly,its this extra air that gives us the fast idle when cold,it duplicates you slightly opening the throttle manually.During cols running the ecu to some degree ignores the sensors.
.
.Now the green EFI coolant sensor on the head tells the ecu when the engine is warm,the ecu now starts to listen to the MAP sensor which says
"throttle partially open" due to the extra air being drawn in via the waxstat.But the ecu is also being told by the TPS
(throttle position sensor) that NO throttle is being applied and this is what throws the ecu into a conflict as it battles between the two sensors to control fuelling.
.
.
.if you listen while its surging you can hear the injectors clicking on and off,MAP says
"more fuel" TPS says
"idling,No more fuel".
Bottom line is you either have air trapped around the throttle body or a stuck open waxstat.
Any solutions ideas?
Somehow I just knew you would know 
and i want 1000 lines 
